Studio Ghibli: “Totoro is not the god of death”
The theory that Totoro is actually the god of death and that Mei was actually already dead has been spreading in Japan for a while. And apparently the makers of the movie, Studio Ghibli has been receiving many calls regarding the truth to this theory.
So to answer this question once and for all, Studio Ghibli has made a statement on their official blog stating that none of it is true. One of the most popular supporting evidences that Mei was already dead was that Mei and Satsuki did not have any shadows at the end of the movie, and Ghibli replies on the blog that they left the shadows out because they decided that they did not need it in the picture at the time.
Of course, it doesn’t really stop the theorists from wondering if they were unofficially making the movie with Totoro as the god of death in mind, and are only stating their official stance as something that is completely different so as not to traumatize the children.